Sawdust absorbs urine very rapidly. In addition, sawdust can absorb and hold a large volume of urine. This greatly slows down the chemical breakdown of urine into Ammonia by bacteria, thereby greatly reducing both the health issues associated with Ammonia and the unpleasant smell of ammonia.

The rapid absorption means that all the urine tends to be absorbed where the horse pees, rather than spreading out and soiling bedding over a large area (a problem which often happens with straw). In addition, sawdust tends to coat and dry out feces, preventing them from soiling a larger area (or sticking to the horse's coat when it lies down). In combination, this means that daily cleaning of a stall requires removal of only a small amount of sawdust and some feces rather than cleaning out all the bedding (which occurs with less absorbent bedding materials such as straw). The associated labour of transporting and storing soiled bedding is accordingly correspondingly reduced, as well as back-filling with clean bedding. Consequently, the labour associated with sawdust bedding is relatively low and one of its major advantages.

Sawdust is normally purchased direct from the sawmill, as other sources tend to be too expensive. Cost varies from low to moderate, depending on circumstances. In many areas there is no demand for the sawdust so sawmills give it away for free to save themselves the cost of disposing of it; in areas where there is a demand (e.g. for horse box bedding) for it the sawmills will charge accordingly. In addition there is the transport fee (which varies depending on the distance from the sawmill) and the need to have sufficient dry storage. Although in some cases (depending on the sawmill and transport costs) the purchase cost of sawdust can be high, this is typically offset by the labour savings described above. As the sawdust typically arrives loose rather than bagged or packaged, one will normally need to shovel it into the storage area, unless there is the possibility of the delivery truck dumping it straight into storage.

Health Issues

The main issue with sawdust is that horses can breathe it in. This can irritate the throat or even cause long-term damage. If it goes deeper, into the lungs, it can cause substantial irritation to them and even long-term damage, to the point that the horse becomes unfit for active work. Even in the circumstances where the horse can be effectively treated, the veterinary bills can be substantial. These risks vary somewhat from horse to horse and depend largely on the amount of sawdust inhaled:

Horses that lay down will tend to breath in more sawdust bedding than those that stand up in their stalls

Horses that are fed in their stalls will tend to breath in more sawdust. Even if they are fed from a pot (rather than on the floor), they will tend to root around on the floor for food that falls down, and thereby inhale the bedding.

Horses in windy stalls will tend to breath in more sawdust, as it is lifted off the floor by air currents.

One also needs to be careful about the type of sawdust, as some types (e.g. Black Walnut) are poisonous to horses; if ingested they can cause serious illnesses. Normally one uses sawdust from white softwoods, or cedar.

Horses which lie down in their stalls can easily push the sawdust to the sides, especially if they roll about, resulting in them lying direct on the floor rather than on bedding. If the floor is cold, during winter this can increase the risk of the horse becoming chilled (which increases the risk of illnesses such as colic). If the floor is hard (e.g. a concrete floor), there can be increased risk of abrasions and similar injuries.

The uniform nature of sawdust provides little mental stimulation for horses, who have evolved to browse most of their waking hours. Consequently, horses confined to their stalls for long periods of time will become bored and consequently mentally stressed quicker with a sawdust bedding than with a straw bedding.

All of the health issues are reduced in the double bedding system. A suitable second layer (e.g. of straw) over the sawdust will tend to reduce the amount inhaled or injested, and stays in place better then sawdust alone. It also increases mental stimulation. However, although this reduces the risk, it is far from eliminating it, and we know of horses which have become seriously ill from sawdust inhalation even in double bedding situations.